A suction ring is fixed to a motor base and is provided with an outer circumferential section having a first outer diameter that is smaller than an inner diameter of a wall section of the motor base. The patient volume observer is operative to estimate a patient volume, that is, the volume actually delivered to the patient by accounting for volume deviation or loss caused by patient circuit leakage and valve dynamics. This method involves providing boron nitride powder and milling the boron nitride powder in a mixture including a milling media and a milling liquid under conditions effective to produce delaminated boron nitride powder. The constellation design accounts for the interrelationship between signal strength and noise in the communication channel.